One of the major contaminants found in crude oil and refinery streams is sulfur. The amount of sulfur found in crude oil typically ranges from 0.001 weight percent to 5.0 weight percent based upon the total weight of the crude oil. Typically, the sulfur is in the form of dissolved free sulfur, hydrogen sulfide, and/or organic sulfur compounds such as thiophenes, sulfonic acids, mercaptans, sulfoxides, sulfones, disulfides, cyclic sulfides, alkyl sulfates and alkyl sulfides.
Since the amount of sulfur permitted in gasoline and other fuels refined from crude oil is regulated by state and federal authorities, fuels produced from crude oil typically contain less than 1.0% to less than 0.05% by weight sulfur. The actual sulfur content of the fuel is primarily dependent upon the sulfur content of the crude oil being refined and the degree of additional processing, such as hydrotreating, that is performed on the refined product. Obviously, it is more expensive to reduce the sulfur content of higher sulfur containing crude oil, thus the production cost of fuels, particularly gasoline and diesel, will be higher for fuels produced from higher sulfur content crude oils.
Typically sulfur from crude oil is eliminated during the refinery process by hydrotreating which requires expensive equipment and creates hydrogen sulfide (H.sub.2 S), a toxic gas that requires additional expense for its safe processing. As a consequence, the price differential between low sulfur and high sulfur crude oil reflects to some extent the capital cost of desulfurization, as well as the increasing demand for lower sulfur fuels.
In view of this background, there obviously is a need for less expensive methods of desulfurizing crude oil and desulfurizing crude oil before it is processed in the refinery. This is particularly true for smaller refineries which cannot afford expensive hydrotreating equipment.